Conventionally, an integrated circuit design is defined by a set of design files contained in a database. Typically, the design of the circuit may evolve during the design process, and the database contains not only the most recent design files, but also an archive of the evolution of the design files. So-called “revision control” is used to track changes made to the design files, and to allow previous versions of a design file to be “re-created” even though the design file may have evolved since.
A version of the files defining a certain significant state of the design is normally identified by a so-called “symbolic tag”. The symbolic tag is an alpha/numeric name with which the versions of the files defining that state are associated. For example, symbolic tags of an evolved design may be called “Version1”, “Version2”, etc. In order to “retrieve” or revert to a certain state of the design, the versions of the design files associated with a certain symbolic tag are accessed through a revision control operation by means of the symbolic tag name. As mentioned above, this enables certain versions or states of the design to be retrieved, even though the design may since have evolved.
However, the above technique has several problems. An integrated circuit is typically designed by one or more teams of designers, who may be spread geographically. Each designer has access to read and modify each file in the database, in order to develop the design. Such reading and modification often involves accessing the symbolic tags, and modifying respective files. This allows significant file versions to be accidentally disassociated with a symbolic tag, or for an association to be overwritten accidentally. Furthermore, integrated circuits are becoming increasingly complex, and require an ever increasing number of design files, whose size generally increases. If associations of file versions with a certain symbolic tag are corrupted as mentioned above, then identifying and correcting this problem is very time consuming and labour intensive. The increasing complexity of integrated circuits also means that the costs of mask preparation used in production are also more expensive for each new generation of a manufacturing process. Often an error which may be caused by a symbolic tag corruption may not be identified until after the production mask has been manufactured, and problems are detected on testing the manufactured integrated circuit. As well as the time and labour involved in identifying the error, correction of the circuit then requires a new production mask to be manufactured, increasing the costs yet further.